A biologically sealed attachment into the wall of the cochlea of a patient that is stable and watertight is often desired, not only for an acoustic actuator, but also for various other medical devices. U.S. Pat. No. 5,951,601 (“the '601 patent”) describes several methods for attaching a microactuator to a fenestration through the wall of the cochlea.
The invention disclosed in the '601 patent has several advantages. A casing locates the hearing device very securely, without vibration. In addition, the invention makes the removal of the hearing device easy, should this be required. Thirdly, together with a precise atraumatic fenestration procedure it provides for a very precise microactuator location, thereby ensuring that the microactuator is optimally situated in the cochlea, without damage to the delicate structures of the inner ear.
Specifically, the casing disclosed in the '601 patent receives a microactuator of an implantable hearing aid system. The casing is implanted into a fenestration that pierces the promontory of the otic capsule bone. The promontory is a projection of the cochlea which is a fluid-filled hearing portion of the inner ear. As described in the '601 patent, the casing is adapted for receiving and attaching to the subject either a microactuator included in the implantable hearing aid system, or a dummy plug to replace the microactuator should removal of the microactuator become necessary. Upon application of an electric signal to the microactuator, the microactuator directly stimulates fluid within the inner ear, which stimulation the subject perceives as sound.
A casing for attaching a microactuator of an implantable hearing aid system to a fenestration formed through a subject's promontory in accordance with the disclosure of the '601 patent includes a sleeve that has an outer surface. During implantation of the casing, a first end of the sleeve is received into the fenestration. Disposed in that location, the outer surface of the sleeve mates with the fenestration for securing the casing within the fenestration. The hollow sleeve includes an inner surface adapted to receive a barrel of the microactuator.
The casing also includes a flange that is integral with the sleeve. The flange projects outward from the outer surface of the sleeve about a second end of the sleeve that is located distal from the first end. The flange, through contact either with a mucosa that covers the promontory or with the promontory itself, limits a depth to which the first end of the sleeve may enter into the fenestration.
A casing in accordance with the '601 patent may employ various means for securing the sleeve within the fenestration such as screwing into the promontory or clamping to the promontory. Similarly, such a casing may fasten the microactuator to the casing in various ways such as by a threaded attachment, with screws, with button-and-socket snap fasteners, or with a slotted tongue-and-groove lock. A casing in accordance with the '601 patent may also include a keyway that receives a mating key formed on the barrel of the microactuator for establishing an orientation of the implanted microactuator.
One difficulty in a process for securing a therapeutic appliance into the wall of the cochlea is that the attachment be biologically sealed. Another difficulty in a process for securing a biologically sealed therapeutic appliance into the wall of the cochlea is safely fenestrating the otic capsule bone without damage to the membranous labyrinth or organ of cord and thus, without damage to hearing.